High gain UHF antenna

[RadioKid]

Hey guys,
Ive got a 1.4m fibreglass rod with a UHF base sitting around. I would like to make a high gain UHF antenna with it.
Im not very familiar with antenna construction and wave lengths etc.
Can someone please give me a link or some info on how to make an antenna.
Thanks in advance, Matty

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[Blake]

Well Matty,
It all depends on what type of antenna you want.
There are dipoles, monopoles, yagis, discones etc. etc.

At the moment I'm actually in the throws of constructing a 9db gain Collinear UHF CB antenna as my new base station antenna for home. I must get some pics of it so far up in a new thread. It currently 1800mm (the main driven elements), but it still needs an elevated ground system / counterpoise and a pigtail for the feedline-- so maybe about 2m when it's all said and done.


By the sounds of it, you're looking at making a monopole around a fibreglass former?
Maybe someone else can chime in with designs and stuff?
There should be formulas / calculators for this stuff.

Oh, if you want a copy of my plans / workings for my Collinear, just drop me a PM mate.
Cheers.

[Nunya-Biz]

Only two questions to ask, before we can get you well on your way ;

1) - Is the Antenna going to be used for both TX, ( transmit ) and RX ( receive ), or just RX only?

2) - Where specifically in the UHF Band, ( what frequency / frequencies ), are you looking to formalise this antenna construction project around?

Let us know, and we'll have you on your way quick smart -

[RadioKid]

Thanks guys for the responses,
The antenna will be RX/TX for 477MHz. Maybe around 6-9db.
That is the 1.4m fibreglass rod I want to use. So the design will be monopole.

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[Nunya-Biz]

Nice pic.

Just need a little more info though…

Is this fibreglass rod 'solid' or is it actually a hollow former?
Another photo perhaps, ( of the other end in particular ) - will be really helpful.

And one lucky last question that'll wrap up the resulting direction your build will take ;

How do you rate your construction abilities / capabilities?
Reasonable Workshop and/or good selection of Hand-Tools?
Powerful ( 60W or greater ) Soldering Iron?

The answer to these will ultimately determine which design and construction pathway is best suited -
( I have good ideas for both a Kitchen-Table build, as well as an 'all-out' proper Workshop build to boot… )

Let us know -

[Blake]

Yeah, I was curious about that too.
As in, is it a former (solid rod), or a cover (hollow).

[RadioKid]

It is a solid fibreglass rod with a 5/16 base.
Im ok with a soldering iron.
I dont have a SWR meter.
I have many tools including pliers, screwdrivers, tap and die, etc.
My abilities are ok. I built a TV antenna that worked and many dipoles for UHF/VHF.
Hope thats helps guys


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[Nunya-Biz]

RadioKid,

Thanks for your recent response, thus finally clarifying the best solution to your original request.


Only two possible solutions I can see as relevant, as to giving you some form of a reasonable outcome are as follows ;

1) - A quick’n’dirty collinear, made from 1/2 wave sections of Coax -

2) - A super quick’n’dirty 1/2 wave, centre-fed dipole, ( with the additional possibility of including a de-coupling sleeve at its Base - making it an elevated-feed, 1/2 wave centre-fed dipole... ) -


Now, given the limited length of your fibreglass solid rod, the ultimate gain achievable from option one - would be limited to around 6dBi.

Option one’s construction complexity would be in the order of four times greater than option two, and is additionally fraught with the added dilemma of how to achieve correct minimisation of common-mode current - from flowing back down the coax...

Option two however, is really, really, REALLY quick to build.

Its design strategy additionally addresses common-mode current, and its performance also is irrefutably the best when considered as, ‘the ultimate all-round performer’...
( Hard to argue, when for almost forever now - this is the solution utilised on just about every single Public Safety Vehicle in Australia, per UHF Comms. )


For the sake of brevity, ( and to save simply reiterating what has already been littered all over the Internet anyway ), I’ll supply a couple of links to get you on your way ;

Option ONE -

http://www.k5frc.org/training/coliner%20antenna.pdf
http://www.rason.org/Projects/collant/collant.htm


Option TWO -

http://w6nbc.com/articles/2009-07QSTcoaxialdipole.pdf
http://vk2zoi.com/articles/half-wave-flower-pot/


Have a tickle within your favourite Search Engine for more examples of the above, ( along with more theory surrounding each design ), and you will discover the almost endless rhetoric concerning these particular antennas.

Either solution can be readily scaled for 63cm, ( read UHF CB ), and I - along with plenty of others in here - would be more than happy to assist you with this issue, once you have settled on a specific design.

Feel free to ask more questions concerning the merits and pitfalls of either solution instead - as to open up this topic for further discussion and dissemination, will only result in more antenna theory thus broken down to the benefit of all within this forum to boot.

Me - OUT
(c;=

[RadioKid]

Thanks again Nunya-Biz,
Im looking for a better looking long term antenna, so im gonna go with the colinear.
If im successful in my first antenna, ill try building ones for different bands. Air, 27MHz, 78MHz, etc.
Cheers guys!! Thanks for the help!

[Nunya-Biz]

No dramas.

Either send Blake a PM for the plans of the UHF CB Collinear which he already has underway, or come back here and ask for some help regarding the necessary 'scaling' for any alternate design you come across - if you feel the need.

( Don't forget to include a method of arresting common-mode current into whatever design you settle on though!
This is an often overlooked issue with this style of antenna… )

Let us know how your build progresses -